1. Field of the Invention
The present invention relates to a machine which can be pulled through and positioned within a pipe or pipeline by a commercially available internal pipe tractor and which is employed to spray liquid coating material onto the interior walls of the pipe or pipeline or onto the interior surfaces of girth welds of the pipe or pipeline.
2. The Prior Art
Preliminary searches were conducted on the invention disclosed herein, and the following patents were uncovered in the searches:
______________________________________ Pat. No. Inventor Issue Date ______________________________________ 1,988,329 A.G. Perkins Jan. 15, 1935 2,158,579 A.F. Hodgkins, et al. May 16, 1939 3,017,855 W.T. Ranker Jan. 23, 1962 3,071,107 R.C. Stanley Jan. 1, 1963 3,753,766 Brown, et al. Aug. 13, 1973 4,092,950 Hart June 6, 1978 4,340,010 Hart July 20, 1982 4,938,167 Mizuho, et al. July 3, 1990 ______________________________________
For pipelines constructed of metal which transport liquid material, contact with the liquid material causes corrosion to the internal surface of the pipeline. Even gas pipelines accumulate condensate which contacts the internal surfaces of the pipeline causing corrosion. To prevent this corrosive contact, pipes are usually coated at the factory with a protective coating. However, the pipe joints where the pipes are welded together, also known as girth welds, are not coated and must be coated after the pipeline is in place. Also, uncoated pipes must be coated to prevent corrosion.
Early devices for applying protective coating material to the inside of pipes consisted of means for centrifugally forcing the coating material onto the interior of the pipe and then troweling the coating material into place. One such device utilizing this means of application is shown in U.S. Pat. No. 1,988,329. One of the problems with this type of application is that the resulting coating is not uniform in thickness.
Another method for applying a protective coating material to the inside of pipes is shown in U.S. Pat. No. 2,158,579. Here the coating is brushed onto the inside of a pipe. Again, the brush bristles do not apply the material in a uniform manner and the resulting coating may have gaps and runs.
Other devices for applying coating materials simply sling the coating material radially outward against the pipe wall. Examples of these types of devices can be seen in U.S. Pat. No. 3,017,855, 3,071,107, 3,753,766 and 4,938,167. Again, the problem with these devices is that the thickness of the material on the pipe cannot be adequately controlled. The present invention utilizes a spray gun to apply the liquid coating material, thus providing a coating of more uniform thickness than previously achieved by other devices.
Mr. Robert J. Hart, a colleague of the present inventor, has two patents on internal pipe coating apparatuses, U.S. Pat. No. 4,092,950 and U.S. Pat. No. 4,340,010. In each of these patents, the material to be applied is a powder. Application is by arms or applicator heads which blow the powder onto the internal surface of the pipe. The present invention differs from these inventions in that it applies a liquid coating material using a spray gun.
Another problem with prior coating devices can be seen in U.S. Pat. No. 3,071,107. This patent utilizes packing seals to prevent leakage between a stationary source of coating material and a rotating nozzle which applies the coating to the interior of the pipe. Packing seals can leak or fail entirely as the rotating member wears against the seals. The present invention solves the problems of packing seal leakage and failure by conveying coating material from a stationary source to a rotating spray head utilizing a rotary fluid coupling capable of having one of its two ends remaining stationary while the other end rotates with the rotating spray gun.
Another problem with previous devices can be seen in U.S. Pat. No. 4,092,950. This device has a shaft which rotates but its rotation is actuated when the coating cycle is initiated. Stopping and resuming shaft rotation causes non-uniform thickness in the coating because the shaft is not rotating at a uniform speed during the entire spray cycle. The present invention solves this problem by continually rotating the shaft and spray gun and turning the spray gun off and on by means independent of the means for rotating the shaft and spray gun.